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Low birth weight may be linked to traffic pollution

Traffic noise appears to have little effect on babies’ weight

Adrian O'Dowd

Wednesday, 06 December 2017

Air pollution from road traffic could be damaging babies’ health in London and other major cities before they are born, suggests a study* published today by The BMJ.

Researchers found that exposure to air pollution from road traffic in London during pregnancy could be linked to an increased risk of low birth weight in babies born at full term, but traffic-related noise seemed to have no effect.

Previous studies have shown associations between air pollution, pregnancy complications and childhood illness, but studies into noise pollution during pregnancy have provided conflicting results.

A team of London-based researchers led by Imperial College London, therefore, set out to investigate the relation between exposure to both air and noise pollution from road traffic during pregnancy and two birth weight outcomes - low birth weight (less than 2,500g) and being born small for gestational age.

They used national birth registers to identify 540,365 live, single, full-term births occurring in the Greater London area between 2006 and 2010.

The mother’s home address at time of birth was recorded and average monthly concentrations of traffic related pollutants – nitrogen dioxide (NO2), nitrogen oxides (NOx), and fine particulate matter (PM2.5) from traffic exhaust and non-exhaust sources – as well as larger particulate matter (PM10) were estimated. Average day and night-time road traffic noise levels were also estimated.

Using statistical models to analyse the data, the researchers found that increases in traffic related air pollutants – especially PM2.5 – were associated with 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age, even after taking into account road traffic noise.

Results showed no evidence that increasing road traffic noise exposure was independently associated with birth weight but the authors said: “We cannot rule out that an association might be observed in a study area with a wider range of noise exposures.”

The authors said: “Our findings suggest that air pollution from road traffic in London is adversely affecting foetal growth.”

They said the annual average concentration of PM2.5 in London in 2013 was 15.3 μg m3, and estimated that reducing London’s annual average PM2.5 concentration by 10% would prevent approximately 90 babies (3%) being born at term with low birth weight each year in London.

They concluded: “With the annual number of births projected to continue increasing in London, the absolute health burden will increase at the population level, unless air quality in London improves.”

In a linked editorial,** researchers at the University of Edinburgh said that though these results from the UK were concerning, “a global perspective reveals something approaching a public health catastrophe” and argued that only policy makers had the power to protect women and unborn babies.

Using the example of Beijing, where air quality levels were improved during the 2008 Olympics, as an example of what could be achieved with coordinated action, they said: “The challenge is to maintain reductions in the longer term through combinations of national and local authority action, particularly around reducing congestion and implementing interventions to tackle diesel combustion emissions in urban areas.”

* Toledano M, et al. Impact of London's road traffic air and noise pollution on birth weight: retrospective population based cohort study. BMJ 2017;359:j5299. DOI:10.1136/bmj.j5299

** Stock S, Clemens T. Traffic pollution is linked to poor pregnancy outcomes. BMJ 2017;395:j5511. DOI:10.1136/bmj.j5511.

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